Born in Bad Kreuznach on the Nahe, Germany on Nov. 18, 1863. After being drafted into the German army, Mannheim deserted and fled to France where he studied art at Ecole Delecluse, Académie Colarossi, and with DeLancey and Bouguereau. Having learned book binding early in life, he used this trade to support himself while studying art in Paris.

Upon immigrating to Illinois in 1884, he painted portraits in Chicago and taught in a Decatur art school. About 1903 he accepted a position at Frank Brangwyn's school in London and stayed for two years. Returning to the U.S., he taught at the Denver Art School until 1908. He then made his final move to Pasadena and built a home in the Arroyo Seco. Mannheim maintained a studio in the Blanchard Building in Los Angeles where he exhibited and taught, and in 1913 founded the Stickney Memorial School of Fine Arts in Pasadena. His figure studies and landscapes prior to 1915 were tighter and done with a restricted palette; whereas, his palette then lightened and he adopted the loose brushwork of Impressionism. He died in Pasadena on Sept. 6, 1945.